What is the term for a negatively charged ion formed by gaining electrons?

A negatively charged ion formed by gaining electrons is called an anion. The process involves an atom or molecule acquiring additional electrons, which results in a net negative charge due to the excess of electrons compared to protons. This contrasts with cations, which are positively charged ions formed by the loss of electrons.

In the context of atomic structure, ions—both anions and cations—are important for understanding chemical reactions and bonding. The term "ion" is a broad category that encompasses both negatively and positively charged particles; however, it doesn't specifically denote the negative charge, which is why "anion" is the precise term needed in this case.

Understanding the significance of anions is crucial in areas like chemistry, where they play vital roles in the formation of salts and the conduction of electricity in solutions, as well as in biochemical processes.